1. Field of the Invention
The invention relates to free-standing water-soluble polymeric films and more particularly to such films in the form of pouches and containing alkaline or borate-containing cleaning compositions.
2. Description of Related Art
A great deal of art relates to water-soluble polymeric films including polyvinyl alcohol. Much of the art has been addressed to the problem of packaging materials in such water-soluble films. As used herein, the term film describes a continuous, homogenous, dimensionally stable polymer having a small thickness in relation to area. As also used herein "polymer" means a macromolecule made up of a plurality of chemical subunits (monomers). The monomers may be identical or chemically similar, or may be of several different types. Unless a more specific term is used, "polymer" will be taken to include hetero- and homo-polymers, and random, alternating, block and graft copolymers. "Copolymer" will be used to specifically refer to those polymers made from two different repeating chemical monomers. An effective water-soluble package would simplify dispensing, dispersing, slurrying, or dissolving materials contained within, as the entire package could be dumped into a mixing vessel without the need to pour out the contents. Water-soluble film packages could be used where the contents are toxic or messy, where the contents must be accurately measured, or maintained in an isolated environment, and further allow delivery of materials which are only metastable when combined, and which would ordinarily separate during storage. Soluble pre-measured pouches aid convenience of consumer use in a variety of applications, particularly those involving cleaning compositions. Such cleaning compositions may include, for example, detergent formulations for ware-washing applications, detergent compositions for washing of clothes, and laundry additives such as peroxygen bleaches, fabric softeners, enzymes and related products. Pouching cleaning compositions presents the added problem of highly-alkaline contents which can interact with polyvinyl alcohol (PVA) films, which surprisingly severely reduces their solubility, strength, or both. The presence of borate in cleaning compositions (e.g. those containing perborate bleaches) can cause cross-linking of the PVA, reducing its solubility in water. The prior art has attempted to minimize the deleterious effects of borate ions by including a borate scavenger such as sorbitol in the film formulation.
The use of PVA films to contain cleaning compositions is further hampered by variations in solubility caused by the range of water temperatures employed. PVA films of the art generally exhibit varying solubilities in hot (above about 49.degree. C.), warm (about 35.degree. C.) and cold (below about 21.degree. C.) water, depending on the residual acetate content. In addition to the need for rapid film solubility under a variety of wash conditions, the films must be stable over typical storage periods and under a variety of environmental conditions. For example, a film pouch containing a detergent product may be stored under conditions of moderate temperature and humidity, under high temperature and low humidity, or high temperature and high humidity. The latter is not uncommon in certain areas of the Southeastern United States. In high humidity conditions, water can penetrate the film, and if an alkaline detergent is present, can have an adverse impact on the film's integrity. One approach to correcting this problem has been to modify or restrict the amount of alkaline material within the pouch. This can, however, have an adverse impact on the cleaning performance. Another problem with water-soluble PVA film pouches for fabric laundering is the adverse effect of the PVA on cleaning performance.
U.S. Pat. No. 3,892,905 issued to Albert discloses a cold-water soluble film which may be useful when packaging detergent. Albert, however, does not solve the problem of insolubilization due to alkaline or borate-containing compounds. Great Britain patent application 2,090,603, to Sonenstein, describes a packaging film having both hot and cold-water solubility and made from a blend of polyvinyl alcohol and polyacrylic acid. The acrylic acid polymer acts as an alkalinity scavenger, but as the acrylic acids become neutralized, the blend loses its resistance to alkalinity and becomes brittle. The polymers of Sonenstein are not compatible, and preferably are made separately, then blended. This means an extra process step, and the blend may result in a poor quality film. Dunlop, Jr., U.S. Pat. No. 3,198,740 shows a cold-water soluble detergent packet of PVA containing a granular detergent having a hydrated salt to maintain moisture in the film, but without apparent benefit to solubility. U.S. Pat. No. 4,115,292 issued to Richardson et al shows compositions with enzymes embedded in water-soluble PVA strips, which are in turn encased in a water-soluble film pouch which may be PVA. Lowell et al, U.S. Pat. No. 3,005,809 describes copolymers of PVA with 4-10 mole percent of a crotonic acid salt from which films can be made to package neutral, chlorine-liberating compounds. Lowell et al does not teach or suggest any solubility benefits when the films are used to package alkaline or borate-containing detergent compositions.
Inskip, U.S. Pat. No. 3,689,469 describes a hot-water soluble copolymer of about 100% hydrolyzed vinyl acetate and about 2 to 6 weight percent methyl methacrylate, and is made to minimize the presence of acid groups. The copolymer can be hydrolyzed using a basic catalyst to form lactone groups, and has utility as a textile yarn warp-sizing agent. Neher, U.S. Pat. No. 2,328,922 and Kenyon, U.S. Pat. No. 2,403,004 disclose copolymers of vinyl acetate and acrylic esters, and teach lactone formation to obtain insoluble films. Takigawa, U.S. Pat. No. 3,409,598 teaches a process for formation of a water-soluble film using a copolymer of vinyl acetate and an acrylic ester. U.S. Pat. Nos. 3,513,142 issued to Blumberg, and 4,155,893 issued to Fujimoto disclose copolymers of vinyl acetate and a carboxylic ester-containing comonomer. Schulz et al, U.S. Pat. No. 4,557,852 describes polymeric sheets which do not include polyvinyl alcohol, but are addition polymers containing high amounts of water-insoluble monomers such as alkyl acrylates and water-soluble anionic monomers such as acrylic salts, and is directed to maintaining flexibility of the sheet during storage. Kaufmann et al, U.S. Pat. No. 4,626,372 discloses a PVA film having a polyhydroxy compound which reacts with borate to afford the film good solubility in the presence of borate. Roullet et al, U.S. Pat. No. 4,544,698, describes a PVA and latex combination used as gas-tight moisture resistant coating agents for packaging materials. The latex may include acrylates or methacrylates and vinylidene polychloride polymerized with acrylate, methacrylate or itaconic acid.
The problem of enclosing an alkaline or borate-containing laundry product in a water-soluble pouch, which is sufficiently strong for a commerical product, remains storage stable for durations and under environmental conditions typically encountered, and remains water-soluble over a range of wash/rinse temperatures typically encountered in the household, has not been successfully resolved. Accordingly, it is an object of the present invention to provide a water-soluble film and process for making the same which retains its water solubility in the presence of an alkaline or a borate-containing cleaning composition.
It is another object of the present invention to provide a free-standing film which is water-soluble and stable during storage over a wide range of temperatures and humidities.
It is another object of the present invention to provide a water-soluble film which can be used to package a cleaning composition and does not have deleterious effects on the performance thereof.
It is yet another object of the present invention to provide a dissolvable laundry additive packet which can be used with alkaline or borate-containing laundry additives.
It is another object to provide a pre-measured, conveniently packaged dose of cleaning composition which is easily stored, handled and delivered to a washing machine, and will rapidly release the cleaning composition into the wash liquor.